Reinforcing Design-Cast 62 with Aggregates

DC-62 must be reinforced either by laying up with fiberglass, or by adding aggregates or fillers. Use aggregates when you want to cast the piece solid.

You can add aggregates such as sand, fine stones, crushed glass, perlite, Styrofoam^® particles, or almost any inert granular material, to DESIGN-CAST mixes in amounts up to 2 parts of aggregate (by volume) for each part of dry mix.

Reasons for using Aggregates

• An aggregate is used when you want a special appearance or texture on the surface of the piece. The incorporation of crushed stone such as marble or granite will produce a piece with a more stone-like appearance and feel.
• In order to attain the best properties (i.e. strength, freedom from cracks, maximum exterior durability) you should incorporate one or more aggregates in a thick piece, or in one which is not uniformly reinforced by fiberglass. In this case you should use at least one part of aggregate for each part of DC-62 dry mix.
• If you want to fill a hollow piece with a heavy or light weight material to make it solid, you can use a heavy or light weight aggregate added to the DESIGN-CAST mix as a compatible fill material. Suitable lightweight aggregates are perlite, or Styrofoam^® particles.
• Aggregates can be used to reduce the material cost in large or thick castings.

Types of Aggregates to use

The aggregate should be granular or coarse in size, and free from very fine or pulverized materials. Typically all the material should be coarse than about 80 mesh.

Don’t use an aggregate in layers of the casting which also contain fiberglass. YOU CAN USE AN AGGREGATE IN A SURFACE COAT WHICH IS BACKED UP BY A COAT OF FIBERGLASS-REINFORCED DESIGN-CAST 62

Don't use a filler like vermiculite, which has a high water absorption, or which otherwise makes the DESIGN-CAST mix too thick or too stiff to work with.

Recommended Aggregates

• Coarse sand or fine stones
• Crushed marble, quartz, granite or other dense rock (Do not use pulverized marble or limestone, or marble dust, since these materials will thicken the DESIGN-CAST mixes excessively)
• Ceramic or porcelain grog, screened to remove material finer than 80 mesh size
• LIGHTWEIGHT: perlite or Styrofoam^® particles
• METALLIC: powdered steel, bronze, and other copper alloys CAUTION: DO NOT USE ALUMINUM POWDER OR FLAKE! ALUMINUM REACTS WITH DESIGN-CAST MIXES.
• TRANSPARENT: crushed glass, glass beads—colored or uncolored

Mixing and Incorporating Aggregates

1. Following the procedure given earlier in this bulletin, mix up a batch of DESIGN-CAST 62 using dry mix, polymer, water, and pigment if used.
2. Then stir in the aggregate manually—or mechanically at a slow speed—until uniformly mixed. You can add as much aggregate as will still keep the mix workable, and will not cause noticeable air entrapment.
3. Pour the aggregated mix into the mold, avoiding air entrapment. To help prevent air pockets, fill the mold in portions, using vibration or tamping between successive additions of mix.
4. Finally, proceed with curing and finishing, as described later in this documentation.

Exposure of Aggregate

After the aggregated mix hardens, the aggregate remains hidden below a thin surface layer of DESIGN-CAST, unless steps are taken to expose it. Aggregate color and texture can be exposed by one of the following methods:

• Grind or sand the surface with an abrasive grit such as coarse sand paper
• Sand-blast the surface until you reach the desired depth of exposure of aggregate
• Brush on a 1:1 mixture of muriatic acid and water, and allow the acid to etch the surface for a few minutes
  CAUTION: MURIATIC ACID IS HAZARDOUS!
  Always follow the supplier's proper handling instructions when using this acid!

When using any of the methods above, scrub down and rinse the surface with water afterward in order to remove the particles loosened by the treatment. Finally, coat the surface with a clear, weatherproof sealer, such as DESIGN-CAST AA-6 or AA-7.

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